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Feb. 10, 1931. MUGDAN AL 1,792,113

PROCESS FOR OBTAINING CONGENTRATED ACETIC ACID Filed March 9, 1929 DILUTE OHgCOOH oomTm vzn I :xTRAoTmG F AGENT CONTAINER 'i' x coruosusso axmnc rwo nann- CONTAINER I ru c. F F'RHCTIONRI'ING 44'' X COOLER 4 HEAT Eater-muss? $R'IRRING V:

PUMP o o o o o o $114.1. com-Jam- Tkfi'rsb c n coqu INVENTORS #ML M Patented Feb. 10, 1931 UNITED STATES a conrom'rron or GERMANY PATENT OFFICE m'rm' M-UGDAN Am J osnr wnmna, or :uumcn, GERMANY, assronons reconsonrrum mm ntnx'rnocnnmscnn mnus'rnm, a. m. B. 11., onmumcn, GERMANY,

maomass non. onremme concnn-rnn-rnn Acnrrc non) Application filed larch 9, 1929, Serial No.

It is known that glacial acetic acid can be obtained from aqueous acetic acid by repeated extraction of the latter bE means of an organic solvent (compare .Galitzensteln, Zeitschrift f. an ew. Ghemie29, page 148). For this process 0 lorinated hydrocar ons are advantageously used as the extractinglagent. The disadvantage of the rocess is t at the distribution equilibrium etween the acetic acid solution and .extracting agent is either very unfavourable, so that repeated extractions and in consequence a large quantity of extracting agent are necessary in order to extract the acetic acid thoroughly, or large quantities of water are dissolved together with the acetic acid by the extracting agent, so that highly concentrated acetic acid cannot be obtained. v

The. present invention relates to a process by which ina single extraction the-whole of the acetic acid is extracted by a comparatively small proportion 'of solvent and at the same time the whole of the water is separated in the form of ice free from acetic acid. For this purpose, the dilute acetic acid in presence of a solvent for acetic acid is cooled to a very low temperature, at least as low as -20 C. and advantageously to the freezing point of the eutectic composed of acetic acid and wa-' ter, namely about -27 C. The acetic acid is separated from the water by any solvent for acetic acid, when the extraction is conducted at the said low temperature, better than when it is conducted at the ordinary temperature. Preferred solvents are those which, while they have a sufiicient solubility for acetic acid, have a low solvent power for water, for instance chlorinated hydrocarbons, in particular dichlorethylene, trichlorethylene, dichlormethane or tetra chlorethane, and esters, particularly acetic acid esters, and acetone oil or the like. Mixtures of solvents, for instance ethylacetate and a hydrocarbon or a. chlorinated hydrocarbon may also be use Emmple 1000 parts gby weight of acetic acid of 40 per cent. strength are thoroughly mixed with dichlorethylene while cooling 345,814, and ln Germany March 19, 1928.

to about -27 C. until no more ice separates.

The water is then in the form of ice free from acetic acid, while the acetic acid is in solution in the dichlorethylene with only a very small proportion of water The ice is separated from the extract in a centrifuge, filterpress or like device, sufliciently protected against access of heat, and is washed free.

from acetic acid by means of dichlorethylene cooled to alow temperature The ice and cold extract are used for pre-cooling further quantities of acetic acid and solvent or for cooling the condenser of a freezing machine. Other known solvents or mixtures of solvents for acetic acid may be used instead of dichlorethylene with good result. Obviously, the

In orderto prevent formation of ice onthe cooling surfaces of the extraction apparatus whereby transmission of heat and the transformation of the ice in the .filtering devices are affected, the process is advantageously conducted in such a manner that the solvent,

which is kept in constant movement is first cooled to a temperature below 2 7 and is then gradually mixed with the pre-cooled dilute acetic ac d, while maintaining the temperature at the said degree. In this case the ice does not separate on the cooling surfaces themselves but within the extracting agent.

The accompan 'ng diagram illustrates how the process may be practlsed. a is a stirring vessel having a coohngj'acket. 'b is a pump.

a is a low temperature cooler. at is a centrifuge or other separating device. 0 is a heat exchange device. f, g and h are containing vessels.

All these apparatus are protected against loss of cold. I r

i is a fractionating apparatus. 7

The extracting agent contained in g is run into a and is circulated by means of pump 1;

through the cooler 0 until its temperature is below -26 C. While maintaining this temperature, the dilute acetic acid is gradually is free from acetic acid and then flows intothe fractionating apparatus, where the dichlorethylene is separated from the acetic acid. The dichlorethylene which has been cooled to a low temperature is first used for washing out the contents of the centrifuge. The ice charged with the solvent is most suitably melted in the centrifuge itself, and its coldness can be utilized anew, for example, by circulating pure solvent through the centrifuge and along the condenser of a refrigerating machine, thereby transferring the warmth of the latter to the ice, which is thus melted. Or else, the centrifuge may be cleared of the ice, and the coldness of the latter otherwise employed.

The solvent contained in the watercan be separated from it by distillation, most convenientlyin order to economize -warmth in avacuum, and, in this case, the solvent should be preferably condensed after having passed through the vacuum-pump. Or else, the solvent can be separated from the water by extracting it through the agency of an-.

other solvent which has a higher or lower boiling-point. Furthermore it is possibleto employ, in the place of fresh water, the wa-.

ter containing the solvent at that stage of the process involving the dilution of the acetic acid (e. 'g. for the precipitation of celluloseacetate). If the diluted acetic acid still contains mineral acids, the latter can best be neutralized before they are submitted to the process herein described by alkali acetate or 4 alkali carbonate.

What we claim is:

1. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous I acetic acid is treated with a solvent for acetic acid is treated with a solvent for acetic.

acid at below minus 26 C.

3. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous acetic acid is treated with solvents containing chlorinated hydrocarbons at below minus 4. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous acetic acid is treated with solvents containing CllOIlIlZtted hydrocarbons at below minus 26 5. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous acetic acid is treated with chlorinated hydrocarbons at below minus 20 C.

6. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous acetic acid is treated with chlorinated hydrocarbons at below minus 26 C.

7. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous acetic acid is treated with dichlorethylene at below minus 20 C.

8. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operation wherein the aqueous acetic acid is treated with dichlorethylene at below minus 26 C.

9. A process for obtaining concentrated acetic acid from aqueous acetic acid by an 10. A process for obtaining concentrated acetic acid from aqueous acetic acid by an extraction operationwherein the solvent is cooled to below minus 26 0., and diluted acetic acid is added gradually, the liquid being constantly kept in motion and the low temperature maintained.

- MARTIN MUGDAN.

J OSEF VVIMMER. 

